In the process of manufacturing ICs with LSI, VLSI and ULSI, patterned material layers like patterned photoresist layers, patterned barrier material layers containing or consisting of titanium nitride, tantalum or tantalum nitride, patterned multi-stack material layers containing or consisting of stacks e.g. of alternating polysilicon and silicon dioxide layers, and patterned dielectric material layers containing or consisting of silicon dioxide or low-k or ultra-low-k dielectric materials are produced by photolithographic techniques. Nowadays, such patterned material layers comprise structures of dimensions even below 22 nm with high aspect ratios.
Photolithography is a method in which a pattern on a mask is projected onto a substrate such as a semiconductor wafer. Semiconductor photolithography typically includes the step of applying a layer of a photoresist on a top surface of the semiconductor substrate and exposing the photoresist to actinic radiation, in particular UV radiation of a wavelength of, for example, 193 nm, through the mask. In order to extend the 193 nm photolithography to the 22 nm and the 15 nm technology node, immersion photolithography has been developed as a resolution enhancement technique. In this technique, the air gap between the final lens of the optical system and the photoresist surface is replaced by a liquid medium that has a refractive index greater than one, e.g., ultra pure water with a refractive index of 1.44 for the wavelength of 193 nm. However, in order to avoid leaching, water-uptake and pattern degradation, a barrier coating or a water resistant photoresist must be used. These measures however add to the complexity of the manufacturing process and are therefore disadvantageous.
Beside the 193 nm-immersion lithography other illumination techniques with significant shorter wavelength are considered to be solutions to fulfil the needs of further downscaling of the feature sizes to be printed of 20 nm node and below. Beside e-Beam exposure the Extreme Ultraviolet Lithography with a wavelength of approx. 13.5 nm seem to be the most promising candidate to replace immersion lithography in the future. After exposure the subsequent process flow is quite similar for immersion and EUV lithography as described in the following abstract.
A post-exposure bake (PEB) is often performed to allow the exposed photoresist polymers to cleave. The substrate including the cleaved polymer photoresist is then transferred to a developing chamber to remove the exposed photoresist, which is soluble in aqueous developer solutions. Typically, a developer solution such as tetramethylammonium hydroxide (TMAH) is applied to the resist surface in the form of a puddle to develop the exposed photoresist. A deionized water rinse is then applied to the substrate to remove the dissolved polymers of the photoresists. The substrate is then sent to a spin drying process. Thereafter, the substrate can be transferred to the next process step, which may include a hard bake process to remove any moisture from the photoresist surface.
Irrespective of the exposure techniques the wet chemical processing of small patterns however involves a plurality of problems. As technologies advance and dimension requirements become stricter and stricter, photoresist patterns are required to include relatively thin and tall structures or features of photoresists, i.e., features having a high aspect ratio, on the substrate. These structures may suffer from bending and/or collapsing, in particular, during the spin dry process, due to excessive capillary forces of the liquid or solution of the rinsing liquid deionized water remaining from the chemical rinse and spin dry processes and being disposed between adjacent photoresist features. The maximum stress σ between small features caused by the capillary forces can be described according to Namatsu et al. Appl. Phys. Lett. 66(20), 1995 as follows:
  σ  =                              6          ·          γ          ·          cos                ⁢                                  ⁢        θ            D        ·                  (                                            H                                                          W                                      )            2      wherein γ is the surface tension of the fluid, θ is the contact angle of the fluid on the feature material surface, D is the distance between the features, H is the height of the features, and W is the width of the features.
To lower the maximum stress, generally the following approaches exist:
(a) lower the surface tension γ of the fluid,
(b) lower the contact angle of the fluid on the feature material surface.
In another approach to lower the maximum stress σ for immersion lithography may include using a photoresist with modified polymers to make it more hydrophobic. However, this solution may decrease the wettability of the developing solution.
Another problem of the conventional photolithographic process is line edge roughness (LER) and line width roughness (LWR) due to resist and optical resolution limits. LER includes horizontal and vertical deviations from the feature's ideal form. Especially as critical dimensions shrink, the LER becomes more problematic and may cause yield loss in the manufacturing process of IC devices.
Due to the shrinkage of the dimensions, the removal of particles in order to achieve a defect reduction becomes also a critical factor. This does not only apply to photoresist patterns but also to other patterned material layers, which are generated during the manufacture of optical devices, micromachines and mechanical precision devices.
An additional problem of the conventional photolithographic process is the presence of watermark defects. Watermarks may form on the photoresist as the deionized water or rinse liquid cannot be spun off from the hydrophobic surface of the photoresist. The photoresist may be hydrophobic particularly in areas of isolated, or non-dense, patterning. The watermarks have a harmful effect on yield and IC device performance.
U.S. Pat. No. 7,741,260 B2 discloses a rinse fluid, consisting of at least one component that has the capability of changing the contact angle of the structures from a 40 to at least 70, thus minimizing the pattern collapse of the structures.
Many further additives for cleaning solutions are known from the prior art. However, none of these use a combination of two kinds of additives. By way of example several compounds are proposed in U.S. Pat. No. 7,238,653 B2, U.S. Pat. No. 7,795,197 B2, WO 2002067304 A1, U.S. Pat. No. 7,314,853 B2, JP 4437068 B2, WO 2008047719 A1, WO 2006/025303 A1, WO 2005/103830 A1, U.S. Pat. No. 7,129,199 B2, US 2005/0176605 A1, U.S. Pat. No. 7,053,030 B2, U.S. Pat. No. 7,195,863 B2, DE 10 2004 009 530 A1, EP 1 553 454 A2, US 2000/53172 A1, and US2005/0233922 A1.
U.S. Pat. No. 7,521,405 B2 discloses surfactants that can be used in rinse formulations, like acetylenic diol compounds and many other types surfactants. It is further discussed that the lowest pattern collapse is achieved if the product of the surface tension and the cosine of the contact angle of the surfactant formulation to the photoresist surface and is low.
US 2010/0248164 A1 discloses a rinse solution for preventing pattern collapse consisting of an anionic surfactant, an amine compound like alkanolamines or quaternary ammonium compounds, and water, for preventing the swelling of the patterned critical dimensions.
U.S. Pat. No. 6,670,107 B2 discloses a method for the reduction of defects in an electronic device by using a rinse solution comprising surfactants in a concentration less than or equal to the critical micelle concentration. It is generally mentioned that mixtures of cationic and non-ionic surfactants and mixtures of anionic and non-ionic surfactants may be used.
US 2009/0004608 A1 discloses an anti-pattern collapse detergent formulation, containing a nitrogen-containing cationic surfactant in combination with an anionic surfactant. It is discussed that this combination enables a reduced content of surfactant, thus preventing photoresist swelling, while maintaining a low surface tension.
While reducing the overall surfactant concentration may be advantageous some notable disadvantages of mixing the anionic and cationic surfactants may follow:    1. The formation of insoluble precipitates due to strong interaction between the opposite charged entities and formation of a very hydrophobic complex, which can precipitate out of the formulation, or affect the medium and long-term stability of the anionic-cationic surfactant formulations.    2. In-situ generation of fine particles and aggregates (precipitates) may occur if the anionic and cationic surfactants are in concentrations of near or above the solubility product of the anionic/cationic complex, or due to local variations in concentration.    3. The Cleaning solutions may not prevent dirt, or particle re-deposition on the surface due to reduced capacity of increasing the magnitude of the surface zeta potential as compared to pure anionic, or cationic surfactants.    4. Unpredictable system in terms of system stability and surfactant-surface interaction.